Phosphobetaines are known from the art. They have excellent foaming properties, are wetting agents and detergents, have antistatic activity and can be used as emulsifiers in numerous technical areas. They are tolerated excellently by the skin, irritate the conjunctiva of the eye only slightly and have a low oral toxicity. They are therefore especially suitable for cosmetic preparations for the care of the skin and the hair.
The state of the art includes, first of all, the U.S. Pat. No. 4,215 064. This relates to a phosphobetaine of the formula ##STR3## in which A represents the O--, OM or --O--Y--R(.sup.+) group and
B represents the O-- or OM group, PA1 X.sup.(-) is an anion and PA1 z is a whole number from 0 to 2, with the proviso that only one A or B group can represent O-- and that z has a value that is required to balance the charges, PA1 M is a hydrogen group, an organic group or an alkali, alkaline earth or mono-, di- or triethanolamine cation, PA1 R is an amidamine group. PA1 R.sup.2 is a hydrogen, alkyl, hydroxyalkyl, alkenyl, cycloalkyl or polyoxyalkylene group, PA1 R.sup.3, R.sup.4 are the same or different and represent alkyl, hydroxyalkyl, carboxyalkyl or polyoxyalkylene groups or, together with the nitrogen atom of the tertiary amine group, can form a heterocyclic ring, PA1 n is a whole number from 2 to 12. PA1 R.sup.2, R.sup.3 represent hydrogen or alkyl groups with 1 to 4 carbon atoms, which may be the same or different, PA1 X is an ammonium group of the general formula R.sup.(+) --R.sup.4 R.sup.5 R.sup.6, in which PA1 R.sup.4 represents a hydrogen, alkyl or alkenyl group with 1 to 12 carbon atoms or a --(C.sub.n H.sub.2n O).sub.z H group, in which n=2 or 3 and the sum of all values of z amounts to 1 to 50, PA1 R.sup.5 is a hydrogen, alkyl or alkenyl group with 1 to 20 carbon atoms or a --(C.sub.n H.sub.2n O).sub.z H group and PA1 R.sup.6 is an alkyl or alkenyl group with 1 to 20 carbon atoms or a --(C.sub.n H.sub.2n O).sub.z H group, in which the R.sup.5 and R.sup.6 groups together with the nitrogen may also form a piperidine, morpholine, imidazole or imidazolin ring. PA1 R.sup.2 is a divalent hydrocarbon group with 2 to 10 carbon atoms, the chain of which may be interrupted by one or more nitrogen atoms, PA1 R.sup.3, R.sup.5 are the same or different and represent alkyl or benzyl groups, and PA1 R.sup.4 is an alkyl group with 1 to 4 carbon atoms. PA1 R is an alkyl group with 1 to 4 carbon atoms, the methyl and ethyl groups being preferred.
An example of such a phosphobetaine is ##STR4## in which R.sup.1 is an alkyl group with 7 to 17 carbon atoms.
In the U.S. Pat. No. 4,283,542, the synthesis of these compounds is described in greater detail. According to the claimed method, a phosphate ester of the formula ##STR5## in which Hal is a halogen group and the remaining groups have the above meaning given, is reacted with an amine of the general formula ##STR6## in which R.sup.1 is an alkyl, alkenyl, alkoxy, hydroxyalkyl, aryl or alkaryl group,
If for example ##STR7## is reacted with 3-cocoamidopropyldimethylamine of the formula ##STR8## in which R.sup.1 represents the average alkyl group of the fatty acids from coconut oil, and contains fatty acids with 7 to 17 carbon atoms, the phosphobetaine of the formula above is obtained.
In the U.S. Pat. No. 4,231,903, detergents and cosmetics are described, which are based on the compounds named above.
A serious disadvantage of these compounds, however, consists therein that, as a consequence of the synthesis process, the compounds contain larger amounts of salt in the form of alkali, alkaline earth or amine salt. Removal of the salt is technically cumbersome, and raises the costs of the products. The high salt content makes the synthesis of anhydrous products appreciably more difficult. This salt content can cause increased corrosion when the phosphobetaines are used in the industrial area. When the products are used in cosmetics, the salt content makes the manufacture of the products more difficult and can lead to skin irritations.
The susceptibility of the aforementioned products to hydrolyze is a further disadvantage. Hydrolysis occurs at the C--O--P bridge ##STR9## and causes the phosphate group to be split off.
The German Offenlegungsschrift No. 2,260,326 relates to zwitterionic phosphorus compounds of the general formula ##STR10## in which R.sup.1 represents hydrogen or the methyl group,
The compounds may also be synthesized by reacting a cyclic phosphite of the general formula ##STR11## in which R.sup.1, R.sup.2 and R.sup.3 have the meaning already given, at an elevated temperature with a primary, secondary or tertiary amine of the formula EQU NR.sup.4 R.sup.5 R.sup.6
in which R.sup.4, R.sup.5 and R.sup.6 have the above meaning given. The reaction is preferably carried out at temperature of 60.degree. to 150.degree. C in the presence of a polar solvent.
An example of a claimed compound is ##STR12## The method of the aforementioned German Offenlegungsschrift No. 2,260,326 enables salt-free phosphobetaines to be synthesized. However, these compounds also contain the --C--O--P bridging element, which is susceptible to hydrolysis.